1. Field of the Invention
The present invention relates to an image forming apparatus, a control method of the image forming apparatus, and a computer program product.
2. Description of the Related Art
With the spread of information processing apparatuses such as copiers, word processors, or computers, and other communication equipment, an apparatus that forms images by using a recording head that operates according to ink-jet technology has become widely used as an image forming apparatus that outputs information from these apparatuses onto a printing medium, such as paper. Moreover, with high definition and colorization of visual information in the information processing apparatus and communication equipment, demands for high image quality and colorization of the image forming apparatus are increasing.
An image forming apparatus for meeting such demands generally has a recording device array that is formed by integrating and arraying a plurality of recording devices in order to correspond to the miniaturization of print pixels. The image forming apparatus has a plurality of recording heads, of which each is made by high densely integrating a plurality of ink discharge openings and liquid paths, for each ink of cyan, magenta, yellow, and black in order to correspond to colorization. This is known as printing according to the ink-jet method.
Moreover, there is another printing method that uses electrophotographic technology. Electrophotographic technology is a method for forming an electrostatic latent image on an electrostatic latent image carrier (image carrier) by using a photoconductive phenomenon and attaching a colored charged corpuscle (toner) to the electrostatic latent image by using an electrostatic force to form a visible image.
In recent years, picture quality similar to that of silver halide photography has been demanded in the field of ink-jet technology and electrophotographic technology. Granularity and glossiness are demanded that is similar to that of the picture quality of silver halide photography.
Glossiness problems can be solved by performing printing on dedicated paper having excellent glossiness. On the other hand, because dedicated paper having such glossiness is expensive, there is a technology for performing printing by using transparent toner (transparent powder ink), transparent ink, and the like to cheaply form an image having glossiness similar to that of silver halide photography. Moreover, varnish printing, UV-cured ink printing, and the like have been widely used. In this manner, a technology for improving glossiness is becoming widespread in a comparatively cheap configuration by overlapping transparent toner or transparent ink on regular ink.
Granularity is improved by a half-tone process. In recent years, as in a half-tone process such as dithering or error diffusion, the high number of lines dithering technique and FM (Frequency Modulation) characteristics have been demanded. This reason is that the lower spatial frequency is, in other words, the lower the number of lines dithering is, the higher the responsiveness of a human eye is to easily recognize dots and this leads to show high granularity.
Each pixel of a silver halide photograph is colored at the molecular level. On the contrary, each pixel in ink-jet technology and electrophotography is colored with dots of which each diameter is 20 to 40 micrometers. For this reason, it becomes important that the human eye does not recognize dots in order to create the feeling a photograph is like a silver halide photograph. As a result, the important thing is for a half-tone process such as an error diffusion process or a minimized average error that has the high number of lines dithering or FM dithering and FM characteristics.
Additionally, it is preferable to suppress the variation of concentration to obtain the same picture quality as that of silver halide photography. For example, the variation of concentration can be suppressed by regularly measuring concentration and performing concentration correction on the basis of the measurement. Japanese Patent Application Laid-open No. 2008-254341 discloses such a correction technique. According to Japanese Patent Application Laid-open No. 2008-254341, test patterns having different concentration are formed in accordance with an image formation process upon power-on and every time when the predetermined number of print sheets have been printed, or every time when receiving a request from the user. For example, in the case of a printing process, a test pattern is formed by using a dithering pattern corresponding to the print process. In the case of a copy process, a test pattern is formed by using a dithering pattern corresponding to the copy process. Then, the concentration of the printed test pattern is detected to obtain brightness or a dot area ratio, a γ correction table is corrected on the basis of the brightness or the dot area rate, and the concentration of the input image data is corrected in accordance with the corrected γ correction table to form an image.
Moreover, even if an image forming apparatus is an apparatus that employs electrophotography or ink-jet technology by which a picture of the same quality as that of silver halide photography can be output, printing with only the picture quality of silver halide photography is rare and outputting an image required in a general office is further demanded. Because print images demanded in a general office require high stability and low granularity, it is considered that the high number of lines dithering or FM dithering is used with low frequency unlike silver halide photography. In recent years, because an image forming apparatus that employs ink-jet technology or electrophotographic technology can perform a plurality of half-tone processes, one image forming apparatus can be separately used as an office application and a silver halide photography application.
When transparent ink is used, because surface scattering characteristics are different depending on whether transparent ink is used, correction must be changed depending on whether transparent ink is used. For this reason, because concentration correction must be separately performed in accordance with the presence or absence of transparent ink for each half tone even if the image forming apparatus that employs ink-jet technology or electrophotographic technology performs a plurality of half-tone processes, there is a problem in that it takes a considerable amounts of trouble and the cost of consumables such as paper, ink, and toner is high.